The present invention is directed to a medical device, such as a surgical mesh or stent, having a substrate and a fibrous coating. The fibrous coating is mechanically fixed to the substrate by entangling the fibers with pores, gaps, and/or through-holes located in the substrate. Entanglement is accomplished in a variety of ways including electrospinning nanofibers into a liquid that flows through the holes in the substrate in such a way that the fibers permeate the substrate and thereby mechanically attach thereto, thus forming a nanofiber sheet. The invention is particularly directed to nanofiber coatings, including nanofiber sheets.
A purpose of the nanofiber coating is to prevent adhesions between the mesh and internal organs. Attachment of the nanofiber sheets at the edges is not sufficient, because surgeons often cut the edges away to make the mesh fit the repair site. A typical mesh is made from a knitted sheet of polypropylene fibers, which are heat set so that the mesh retains its shape when subjected to shearing forces. Setting the mesh in this manner also enables it to withstand tensile forces, which is necessary to keep a hernia closed, for example. The coating generally needs to be present only on the side of the mesh that faces the internal organs that are to be protected from adhesions.
Some methods for attaching nanofibers to medical devices are known in the art. These include the use of glue to attach nanofiber sheets to the mesh, and attachment by suturing through the mesh. Unfortunately, using glue introduces additional substances into the body, which may have undesirable side effects. Suturing also presents problems in the sense that it is difficult to hold the nanofiber sheet in place while the mesh is being positioned during suturing. Other methods of coating medical devices with fibrous materials include, dipping, spraying, spin coating, electrospinning, and the nanofibers by gas jet (NGJ) method.
Greenhalgh et al. (U.S. Patent Application No. US 2003/0211135A1) discloses a stent device having an electrospun covering of a fibrous polymer layer. However, the layer is bonded to the device either by applying the polymer wet or by heating the polymer after being applied. In either case the attachment is through adhesion rather than entanglement of the fibers with the substrate.
As suggested above, prior work in the field of coated medical devices has employed a variety of means for attaching the coating to a substrate, but lacks any teaching of mechanically attaching fibrous layers by entangling them with the substrate. The present invention fills this gap in the art by providing several methods for attaching such coatings, and providing devices produced through the practice of these novel coating attachment methods.